Hydraulic transmission



June 28, 1960 M. M. HANN ET HYDRAULIC TRANSMISSION -4 Sheets-Sheet 1 Filed July 31, 1957 June 28, 1960 M. M. HANN ETAL 2,942,421

HYDRAULIC TRANSMISSION Filed July 31, 1957 4 Sheets-Sheet 2 June 28, 1960 M. M. HANN ETAL 2,942,421

HYDRAULIC wmmsmssrou Filed July 31, 1957 4 Sheets-Sheet 3 14/ Z Z7 Z219 June 28, 1960 M. M. HANN ET HYDRAULIC TRANSMISSION Filed July 31, 1957 4 Sheets-Sheet 4 INVENTORS.

many diiferent forms, and it should. be understood that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

According to our invention, a constant pressure, vanable volume system is provided including an arrangeadapted for use with mobile equipment of the slow moving, hard working type, such as lift trucks and the like. Lift trucks of the type referred'to'conventionally include thereona movably mounted lift device, such as a lift fork which is usually mounted for extension and retraetion relative to the lift truck to reach and to withdraw from the load. The lift fork is also mounted for movement up and down on the lift truck to hoist and lower the load.

A typical truck of the type referred to includes a truck chassis or frame, a pair of driving wheels supported by one axle of the truck frame, usually near one end of the truck, one or more guiding wheels supported by the truckframe, usually near the other end of the truck, and means supporting the lift device on the truck frame for movement'as described. The lift device may comprise a lift fork of generally L-shaped configuration including a generally upright leg and a generally horizontal leg, the latter disposed for movement underneath a load, such as a pallet conventionally employed in warehouses and the like for use in transporting stacked materials from place to place in the warehouses with lift trucks of the character described.

The hydraulic system in general The hydraulic system illustrated is adapted to be mounted entirely on the truck frame of a lift truck or the like, and includes means for propelling the truck, means for extending and retracting the lift fork, and means for hoisting and lowering the fork. The system illustrated includes the advantages of a precise and smooth control of each operation provided, with an unlimited speed range for each operation, and with a wide variationvin torque for the propelling operation. The system also provides for extreme flexibility in installation and may be further utilized for providing a source of fluid under pressure for power steering and other auxiliary hydraulically operated attachments.

Referring now to Fig. I particularly, as illustrated, the invention is embodied in a system which includes a pair of hydraulic motors 10 and 11 adapted for connection respectively with a pair of driving wheels of the lift truck for propelling the truck. The motors 10 and 11 are of a variable displacement type in order to provide a wide variation in developed torque, and are reversible in order that the truck may be driven either forwardly or reversely. A third hydraulic motor 13 of a constant displacement type is provided for extending and retracting the lift fork to reach and withdraw from a load, and a hydraulic motor 14 of the reciprocable piston and cylinder type is provided for lifting and lowering the lift fork.

The system includes means providing a source of operating fluid at. constant pressure, comprising a variable displacement pump 15 connected to be supplied from a reservoir 16 and adapted to be driven bya variable speed prime mover 17, such as an internal combustion engine. The pump, the reservoir, and the prime mover are all adapted for mounting on the truck frame and for suitable connection in the hydraulic system. Similarly,

'4 the hydraulic motors 10, 11, 13 and 14 are also adapted for mounting on the truck frame, for suitable connection in the hydraulic system, and for connection with the devices which they operate.

Operations of the propelling motors 10 and 11, the reach motor 13, and the lift motor 14 are controlled respectively by 4-way directional valves, including a propelling valve 18, a reach valve 19, and a lift valve 20 which are connected in the system to control the flow of operating pressure fluid to and from the motors.

Operating fluid under pressure is supplied by the pump 15 to the body of the propelling valve 18 through a line 21, from the body of the propelling valve 18 to the body of the reach valve 19 through a line 22, and from the body of the reach valve 19 to the body of the lift valve 20 through a line 23. In this manner, the directional valves are all connected in series with the source of pressure fluid and in parallel with each other, so that operating fluid under pressure from the source is always available at each of the directional valves 18, 19 and 20.

The respective motors are connected in series with the associated directional valve and accordingly, the motors may be operated separately, or two or more of them may be operated simultaneously with individual control of the speed of each. While the directional valves have been illustrated as separate structures, it will be appreciated that these may all be made, if desired, in a single body, or the three may be separate and arranged in adjacent relationship in a multiple unit valve stack.

The propelling motors 10 and 11 are connected in series with the propelling valve 18 and in parallel with each other. Flow to these motors from the valve 18 is normally equally divided between the two motors so that the power supplied thereto is the same. The circuit between the valve 18 and the propelling motors includes a differential valve means 25 which functions to divide the flow through the motors 10 and 11 when one of the motors encounters a greater resistance to turning than the other, as when one of the truck driving wheels is positioned on a slippery surface such as ice and the other driving Wheel is positioned on a tractional surface. In this case, the differential valve means 25 functions to increase the flow to the motor encountering the greatest resistance to turning and to decrease the flow through the motor having the least resistance ot turning.

The directional valve 18 includes valving described more in detail hereinafter, manually operable, for obstructing the flow of fluid from the propelling motors 10 and 11 thereby to brake the motors when the lift truck is slowed down to a stop or when the truck is parked in neutral on an incline. In order to facilitate the braking of the propelling motors, the circuit connected with these motors includes a braking relief valve means 26, an over pressure relief valve means 27, and a makeup valve means '28, the latter of which functions to maintain the braking circuit charged with a supply of fluid. Also, the propelling motors circuit includes an automatic braking valve means 29 which functions to obstruct the flow of fluid from the propelling motors and thereby brake the motors at any time when these motors require a flow greater than that provided by the source, as when the motors tend to overrun at a time when the truck encounters a downward incline.

As previously noted, the propelling motors 10 and 11 are of the variable displacement type, and this characteristic is utilized to operate the motors either at a minimum displacement, high speed, and low torque, or at a maximum displacement, low speed, and high torque. Operation of the motors in this fashion may be controlled either by a manual torque valve means '30 for controlling the displacement of the motors or by an automatic torque valve means 31 for controlling the displacement of the motors.

System in detail Referring now particularly to' Fig. 2, the pump 15 may pressure" pump discharge. includesta valve body 51 which desirably may be integral with the pump housing endplate 52. Itisibecause :the :control. valve means is provided ::in :thepump end 'lieiof acoust-ructiaa including :a: rotatablecylinder: block 35%suitably'keyed to a pump' dn've shaft'M -for' rotation therewith. The cylinder blockis formed with an" annular series: of axially. disposed cylinders 37 which receive .thereinaxially reciprocal pistons'38' biased outwardly of the cylinder block by springs 38a. The pistons 38, throughthemedium of suitablegbearing shoe apparatus,

bear against an adjustable angleswash plate 39 nonrotatably heldiin the pump housing 40. On rotation of the cylinder block 35, in a conventional manner, the pumpcylinders 37 take fluid in from an inlet conduit 41 through: an intakekidney 42 provided in the pump housing, and through individual cylinder ports 43. The pump cylinders 37 discharge through the individ-uali ports 43, througha discharge-kidney 44 to 'the pump outlet line 21.

The variable angle swash plate 39 normally biased to a minimumdisplacement position by means inherent in its mountingand by means of the piston springs 38a. Means is provided to vary the angle ofthe swash plate, and this means partakesof a displacement varying control piston 46 mounted in a control cylinder' 47 in the pump -housing40, and biased againstthe swash plate by means-ofaspringdii. When the control cylinder 47 is connected to drain, the swashplate' 39 will assume a a minimum displacement position. Control fluid under pressure may be -admitted to the cylinder 47 toincrease the swash plate angle and thereby increase the pump displacement.

Con-trol valve means 56 is'providedto control the flow of pressure fluid to and from the cylinder 47 in response to the pump discharge pressure in the line 21-to thereby .controlthe pump displacement. to produce a constant The :control. valve means 50 plate :52 that the :valve means does not appear separately in the circuit. diagram of Fig. l. The body 51 is formed with abore having a valve sleeve 53 retainedtherein by means-eta snap ring 54. The valve sleeve 3is formed withexternal grooves 56 and 57 which register respectively with ports 58 and 59 in the valve' body 51. The

here is formed with an internal groove 64 which communicates with the external groove 56 through radial ports 65 and an internal groove 66 which communicates withthe external groove 57 through radial ports 67.

The control valve member 63 is normally biased upwardly as illustrated by a spring 68 which normally positions the valve member against a retaining ring 69 in the valve gsleeve bore. When the 'valve is so positioned, the internal sleeve groove 66 communicates with a sleeve bore 71 through external, inverted V-shaped recesses 72 on the valve land 63b. The sleeve bore 71 in turn communicates through a valve member bore 73 with a conduit 7 4 leading from the valve body 51 to the pump discharge line 21. The variable displacement control cylinder 47 is thereby connected to pump discharge pressure.

If the pump is started now, with each of thedirectional valves 18, 19 and 20 closed,'pressure in the line 21 will 'immediatelybuild up. .Such dischargepressure, through the conduit 74, acts against the upper, relatively'large end surface of the control valve mem'berportion 63a to force the valve member downwardly againstthe bias of the spring. ,68 and. the pressure of iluid in the bore 71. Movement of the valve member will continue under these conditions .until such time as the internal sleeve groove 66 communicates with external V-shaped recesses 76 on acting against the upper end 015 thecontrol valve member 63 and the spring 68 is effective to force the valve member upwardly. The variable displacement control cylinder 47 is thereby connectedto-pump discharge pressure through conduit 74, thevalvemember bore 73, the external recesses 72 on the valve member and the conduit 61. Fluid pressure is then efiiective to' force the control piston 46 outwardly of the-cylinder 47, increasing the swash plate angle and the pump displacement.

The operation described is eifective to maintain a substantially constant fluid pressure in the pump discharge line 21.

Referring again to Fig. 1, the'pump-drive shaft 36 is connected to be driven by the prime mover 17 which may comprise an internal combustionengine of a conventional type. 7 The speed of the engine'17 iscontrolled by a fuel feed device such as a carburetor'78. The carburetor is controlled by a mechanism including a lever 79 normally biased by a lea'f spring 80 against an adjustable stop 81 so as to normally supply suflicient fuel to the engine 17 to support its operation atan idle speed.

The carburetor lever '7? is automatically controlled to increase the fuel feed to the engine 17, and thereby increase the engine speed, in response to increased flow in the pump discharge line 21. Control of the carburetor is effected by means of a link 83; connected with the carburetor lever 79 and also connected with the piston rod 84 of a'piston 85 reciprocalin a cylinder 8-6. The piston 85 is normally biased toward'anidl'e position by means ofv a spring '87 which acts in conjunction with the leaf spring '80. a

A restrictive orifice 88 is provided in the pump discharge line 21, and the pressure'drop across the orifice 3-8 is utilized to control the position-ofthe piston 85 in accordance with the flow rate in the pump discharge line 21. To thisend, aconduit89is connected to the pump discharge line 21 ahead of theon'fice 88 and to the cylinder '86 on one side of the piston 85. Another conduit 90 is connected to the pump discharge line 21 down stream of the orifice 88 and is connected to the cylinder 86 on the opposite side of the piston -85.

In response to an increased flow through the line 21, there occurs an increased pressure drop across the orifice 88. The pressure in the line 89 and on the left-hand side of the piston 85 accordingly increases with respect to the pressure in the line 90 and on the light side of the piston 85, forcing the piston to the right, as illustrated in Fig. 3, thereby increasing the speed of the engine i"/'. As illustrated in Fig. 3, this action would occur after one of the directional valves, such as the valve 18, is opened requiring an increased flow. In order to maintain the system pressure constant, the speed of the prime mover is increased along with an increase in pump'displacernent. If now, the valve 18 is closed, the pressure downstream from the orifice 33 will become equal to that upstream of the orifice, and the piston 85 will return toward its original position thereby reducing the speed of the engine'l7.

The load on the engine 17 driving the pump 15 is directly proportional to the flow from the pump. Thus, the means described for controlling the engine speed is effective to sense the pump displacement and to modulate the speed of the engine in accordance with the varying load demands thereon. The design of the piston 85 and the strength of the springs controlling the piston are calculated so as to match the torque output of the engine 7 with the flow requirements of the hydraulic system, and thus permit economic operation of the engine only at a speedrequired for any given'load condition.

As previously noted, pressure fluid from the pump discharge line 21 flows to the body of the directional valve 18, thence to the directional valve 19, then to the valve 20 so that pressure fluid is always available at each of the valves to permit propelling, reaching, or hoisting, either separately or simultaneously. v

The directional valve 19 for controlling the reach motor 13 includes a valve body 92 having an elongated bore 93 which is provided with a centrally disposed annular groove 94. The groove 94 is provided, with an inlet port 95 which communicates with the pressure conduit 22 from the valve 18, and includes an outlet port 96 which communicates with the pressure conduit 23 with the valve 20. The valve body is also formed with a pair of motor ports 97 and 98 disposed respectively on opposite sides of the centrally annular groove 94 and drain ports 99 and 100 near opposite ends respectively of the bore 93. A conduit 101 leads from the motor port 97 to the motor 13, and the conduit 102 leads from the motor port 98 to the motor 13. Drain ports 99 and 100 are connected with conduits 103 and 104 respectively which lead to drain grooves in the valve 20.

A valve stem 105 'is slidably disposed in the valve bore 93. The stem 105 includes three spaced lands including a central land 106, an upper land 107 and a lower land 108. The lands are separated by reduced portions of the stern including an upper reduced portion .109 and a lower reduced portion 110.

The valve stem is biased to a neutral center position illustrated in Fig. 1 by means of a spring 111. The spring bears against a lower collar 112 and an upper collar 113, both slidable on the valve stem and both slidable in an enlarged portion of the valve body bore. The collars 112 and 113 are both adapted to bear against shoulders formed on the valve stem and on the valve body in a manner to permit movement of the valve stem in opposite directions from the neutral center position shown in two operative positions, one for effecting operation of the reach motor forwardly and one for effecting operation of the reach motor reversely. Movement of the valve stem may be effected by manually operable means including a handle 114 pivotally mounted on the valve body structure and having a suitable pin and slot connection with the rod 115 extending upwardly from the valve stem 105.

The reach motor 13 may be of a conventional type including a rotatable cylinder block 117 connected to drive an output shaft 118 and having axially reciprocal pistons 119 bearing against a fixed angle swash plate 120. The construction of the motor 13 is such that it may be operated forwardly or reversely by reversing the direction of flow through the motor.

Operation of the reach motor 13 forwardly is obtained by moving the valve stem- 105 upwardly from the position illustrated in Fig. l to a position in which the stern groove 110 connects the valve inlet port 95 and the motor port 98. In this case, the fluid from the motor 13 flows into the valve 19 through the motor port 97 and passes to drain through the stem groove 109 and the drain port 99. Operation of the reach motor reversely is obtained by movement of the valve stem 105 downwardly from the position illustrated to connect the valve inlet port 95 a with the motor port 97 through stem groove 109. In this case, fluid flows from the motor 13 into the valve 19 through motor port 98, and passes to drain through the stern groove 110 and the drain port 100. The speed of operation of the motor 13 may be controlled by the amount of valve opening movement of the stern 105.

The construction of the lift valve 20 is substantially identical with that of the valve 19, and accordingly will not be described in detail. The elements of the valve 20 which find their equivalents in the valve 19 are identified let port 96 in the valve 19 since none is necessary, the

valve 20 being the last of the group. i

The lift motor 14 may be of a conventional piston and cylinder type including a cylinder 122 having a piston 123 reciprocable therein and having a piston rod 124 adapted to be connected with the lift fork of the lift truck. In order to elevate the lift fork, the valve stem 105' is moved upwardly from the position illustrated in Fig. 1

to a position connecting the inlet poit to the motor port 98 through the stem groove 110, thereby admitting fluid .to the left end of the left cylinder 122 through a conduit 125. At the same time, the right, end of the left cylinder is connected to drain through a conduit 126, motor port 97', the stem groove 109', and drain port 99'. The drain ports 99' and are connected by conduits 127 and 128 which merge and are connected to the reservoir 16 by conduit 129.

'Lowering of the lift fork is obtained by movement of the valve stem downwardly from the position illustrated in Fig. 1 to admit pressure fluid to the right end of the left cylinder 122 and to connect the left end of the cylinder to drain, as will be understood. The speed of operation of the lift motor 14 may be controlled by valve opening movement of the stem 105', or other means may be provided to meter the flow to control the speed.

7 The propelling motors circuit in detail The directional valve 18 for controlling operation of the propelling motors 10 and 11 includes a valve body formed with a central longitudinal bore 136 which includes a centrally disposed annular inlet groove 137. The groove 137 has an inlet port 138 communicating with the pressure line 21, and an outlet port communicating with the pressure conduit 22. The valve body 135 is also formed with a pair of motor ports 139 and 140 disposed respectively on opposite sides of the central annular groove 137. Drain ports 141 and 142 are provided in the valve body near opposite ends respectively of the bore 136.

The motor port 139 is connected with a conduit 144 which in turn is connected with branch conduits 145 and 146 leading respectively to the propelling motors 1-1 and 10. The motor port 140 is connected to a conduit 147 leading to the diiferential valve means 25 which in turn is connected to branch conduits 148 and 149 leading respectively to.the propelling motors 10 and 11.

A valve stem 150 is slidably disposed in the valve bore 136 for movement in opposite directions from the neutral center position illustrated in Fig. l to two operative positions, one for effecting operation of the propelling motors forwardly, and one for effecting operation of the propelling motors reversely. The stem 150 is formed with enlarged portions or lands thereon, including a centrally disposed land 151, two lands 152 and 153 disposed upwardly on the stem from the center land, and similarly, two lands 1.54 and 155 disposed downwardly on the stem from the center land 151. The five lands referred to are separated by outer stem grooves 156, 157, 158 and 159.

Movement of the va ve stem 150 is controlled by means similar to that utilized for controlling the operation of the valve stem 105 in the directional valve 119 and identified by similar reference numbers double primed.

The propelling motors 10 and 11 may be of a similar conventional construction. Since the motors are identical, only motor- 10 will be described in detail. Similar reference numbers are used to designate similar parts in the motor 11 with a prime sufiix. The motor 10 includes a rotatable cylinder block 160 connected to drive the motor output shaft 161. The cylinder block 160 is formed with an annular series of cylinders housing reciprocable pistons 163 which bear against a variable angle swash plate 164.

demand A control piston 165 is;recipr'ocable-.in thevmotor housing to vary the angl'e of theswaslfrplate ld. 1

Gperatio-noi the propel-lingrmotors =and :11 forwardly is obtained by delivering pressure fluid tot-themotor. conduit 147. The differential valve means'ZS normally functions to divide the flow from the conduit 147 and deliver equal flows to the conduits 148 andy149 toobtai-n-iderrtical operation of the motors lfiwand- 1-1. Inorder to obtain operation of the motors 1-0 and ilforwardly, the valve stem 150 is moved downwardly from the neutral center position illustrated in Fig. l tov the position illustrated in Fig. 3 With the valvemember positioned as illustrated in Fig. 3, the fluid under pressure enters the valve. 18 from the. pressure conduitZl at the central valve body groove 137, passes through the stem groove 157 to conduit 16'? which mayif desired be formed in the valve body 135 alongside the main valve bore 136. The fluid passes from the conduit 1-67 into the main valve bore 135, through the stern groove 158,,to themotor port 140, and thence to the propelling motors. The flow from the motors 1t) and 11 passes to conduits 145 and 146, conduit 144 and to the motor port 139." From the motor port 139 fluid passes to drain through stem groove 156, the drain port 141, and a drain passage 168. As illustrated in Fig. 3, thedirectional valve 18 has been moved to afully open position forobta'ining operation of the pro;- pelling motors at full speed in a forward direction.

Operation of the propelling motors .10 and 11 reversely is obtained by movement of the valve stein'15uup-wardly of the neutral position illustrated in Fig. 1 to :the position illustrated in Fig. 10. When the valveis positioned" as illustrated in Fig. 10, pressure fluid flows'fr'oin the pressure conduit 2d to'the valve bore, stem groove 158', conduit 167, and stem groove 151 to the motor port 139." The flow from the motor port 139 is through conduit 144- and branch conduits 145 and 146 which serve to divide the how equally to the two motors. The flow fro-in the motors 1d and 11 passes through branch conduits 148 and149 to the difierentialvalve means 25-,- conduit 147, motor port 140, stem groove 159, drain port-14'2-, anda drai conduit 169. As illustrated inFig. 10, the valve stem is positioned to obtain full speed "operation of the motors 1t? and 11 in a reverse direction. A low speed operation of the motors may be obtained lay-moving the valve stem only sufliciently to obtain a partial valve opening.

It will be noted that the propelling motors lo and 11 are connected in series with the sourceof operating fluid, and. in parallel with each other. With the motors arranged in parallel as illustrated, a .diif'erential action is provided at the motors, whichperrnits .a relative movement between the two when the lift truck is beingdriven and is turned so that one of the driven wheels moves'in an" arc of greater radius than the other.

While the diflerential action thusprovided-gives rise to certain advantages, the connection of the motors in parallel may also give rise to certain disadvantages. More specifically, if one of the driving wheels'is positioned on a slippery surface, such as ice or oil, whi1e the other wheel is positioned on, a tractional surface, the flow of oil from the source will of course take the path of least resistance, and a greater portion of the flow will pass through the motor having the least resistance to turning with the result that the wheel positioned on the slippery surface will spin and the flow to the other motor willbe insuflicient to propel the lift truck. In order to overcome this difliculty, the diiferential valve means 25, previously referred to in general, is provided to produce a diife'rential flow through the motors, providing an increased flow to the motor having the greatest resistance to turning and a decreased flow through the motor I having the least resistance to turning. In this manner, the flow to the motor driving the wheel on a tractional surface will be sufficient to propel the truck.

Referring now particularly to Figs; 8 and 9 for a detailed description of the differential valve 25, it will be seen that the valve'comprises a valve body 175 having '10 a. chamber 176: t'o which'rthe conduit 14'7" Ieads'froin the directional valve 18. The chamber 176 is formed with two ports "177 and 178 which lead to a transversely extending bore. 179 in' the valve body having annular grooves 118i and 181 which register with the ports 177 and 178, respectively. The bore 179 terminates at opposite ends Offtil valve body in chambers 182 and 133 which maybe termed inlet or outlet chambers, and which communicate respectively with motor conduits 148 and 149. A pair of similar sleeves 184 and 185 are positioned one in each of the chambers 182 and 183. The sleeves are retained .in position by retaining rings 186 and 187.

A valve member 189 is slidably positioned in thevalve bore 179 between the two plugs 184 and 185. The valve member189 is normally retained in a centered position by oppositely acting springs 19iiand. 191, each of which bears .at one end against a shoulder on the valve member and at the opposite end against a. shoulder formedon the adjacent sleeve: The valve member 189 is formed with a pair of longitudinally extending bores 195 and 196 openingrespectively at opposite ends of the valve member.

'These bores, 195 and 196, provide orifices interconnecting 191-. With the valve positioned as illustrated in Fig; 9,

it .will be clear: that whether the flow enters the valve body at the chamber 176 orat the chambers 182 and 183, the valve member 189 is positioned such that the flow through the two motors is equal.

If, with the propelling motors 10 and 11 operating in a forward direction, and withthe diflferential valve member 189 positioned as illustrated in Figs. 1, 3, 4 and 9, one of the wheels driven by the propelling motors encounters a slippery surface, the differential valve 25 will come into play. Let it be assumed that with thepro- .pelling motors operating forwardly, the truck wheel driven. by the motor 11 encounters a slippery surface, while the wheel driven .by the motor 10 is on a tractional surface. In this case, the motor 10' under heavy load will have a substantially greater resistance to turning than will the motor 11 which is only lightly loaded. As a consequence, the operating fluid, taking the path of least resistance, flows in substantially greater quantities (ten times greater, for example) to the motor 11 than to the motor-10, leaving insuflicient fluid andpressure to drive motor 10, and the pressure downstream of the orifice 196 falls greatly relative to the pressure downstream-of the orifice 195. This differential pressure, operating against opposite sides of the valve member 189, serves to shift the valve member 189 from the position illustrated in Fig. 9 to the position illustrated in Fig. 8. This movement of the valve member 189, in closing the bore grooves 180 and 181 forms a restrictedorifice, which reduces the flow'of fluid to the lightly loaded motor 11 to a value substantially less than the total flow of fluid from the pump, leaving quantities for flow to motor 10. While the path of flow to the motor 10 also becomes restricted by partial closure of the groove 180, the restrictions in the flow paths of the operating fluid cause an increase in the pressure .of the operating fluid and fluid under higher. pressurewill now flow to the motor 10. The'flow which now passes to the motor 10 will be at suflicient pressure to propel the truck to move it off of the slippery surface. When the motor 11 again is loaded similarly with the motor 10,valve member 189 is returned by the spring 191 to the neutral center position illustrated in Fig. 9.

The amount of fluid which is permitted to flow to the motor 11 when the valve member 189 is positioned as illustrated in Fig; 8, is determined by the amount of movement of the valve member 189 relative to the bore grooves 180 and 181. The amount of valve movement permitted may be regulated by the length of the sleeve members 18 4 and 185 which act as stop members limiting valve movement. The sleeves may be removed and replaced by sleeves of shorter or greater length to thereby vary the length of valve movement permitted and accordingly decrease or increase the size of the restrictive orifices formed at the grooves 180 and 181.

The condition of the circuit and the position of the valve member 189, illustrated in Fig. 8, also represents the circuit conditions when the motors and 11 are driven reversely and the truck wheel driven by the motor 10 encounters a slippery surface with the motor 11 heavily loaded with its wheel on a tractional surface. In this case, the flow of fluid will be to the motors through the conduit 1'44 and from the motors through the conduit 147. Under these conditions, since the motor 10 is only lightly loaded, the flow through this motor is much greater than that through the motor 11. Consequently, the increased fiow through the conduit 148 relative to the flow through the conduit 149 gives rise to an increased pressure in the inlet chamber 182, forcing the valve member 189 to the position illustrated in Fig. 8. 1

If desired, the plugs which limit movement of the valve member may be of a length which will permit movement of the valve member to a position completely blocking the flow of fluid therethrough. In this case, the valve body is formed with passages bypassing the valve member and provided with adjustable orifices which restrict the flow to the unloaded motor when the valve is closed. Such a modified structure is illustrated in Fig. 11, wherein the parts which correspond to similar parts in Fig. 9 have been identified by similar reference numbers with a sufiix x.

As seen in Fig. 11, plugs 1841: and 185x permit movement of valve member 189x to the right or left from the neutral position illustrated, depending on the direction of rotation of the motors and depending on which motor is unloaded, to positions completely blocking the flow of fluid through the valve member. Valve body 175x is formed with passages 192 and 193, bypassing the valve member 189x, and leading from the chamber 176x to the chambers 182x and 183x respectively. The passages 192 and 193 are provided with variable orifices 194 and 194a respectively, which are formed in part by adjustable needle valve members 199 and 19911, respectively. The adjustable orifices 194 and 194a thus would function to meter the flow to the unloaded motor, thereby providing a flow to the loaded motor. The advantage of this construction residm in the fact that the adjustable needle valve members 199 and 199a may be positioned for access exteriorly of the valve body 175x to permit adjustment without the necessity of disassembly.

Also, it will be appreciated that the desired results may be obtained by other valve means as well. For example, means may be provided whereby the flow to the unloaded motor is restricted substantially while leaving the passages to the loaded motor completely unrestricted.

As previously noted, the propelling motors 10 and 11 are variable displacement motors, and this characteristic of the motors is utilized, in combination with the torque multiplication valve means 30 and 31, previously referred to, to obtain the optimum usage of a small prime mover, enabling the reduction in size of a lift truck or the like where maneuverability in close quarters is so essential. With the hydraulic system illustrated, the optimum size prime mover, such as the engine 17, isone that will provide just enough power to maintain the vehicle at full speed with a full load on a level surface with no reserve power to climb an incline or a ramp. The automatic torque multiplication valve 31 enables the practical use of a small prime mover engine by automatically sensing an overload condition on the motors 10 and 11 to automatically increase the displacement of the mo- (12 tors, thereby providing an increased torque output and a reduction of the speed of the motors. Additionally, the displacement of the propelling motors may be controlled manually in order to obtain a low speed operation for inching the truck along at a slow speed.

The torque valve means includes a valve block 200 incorporating both the automatic torque valve 31 and the manual torque valve 30. As illustrated in Figs. 6 and 7, the valve block 200 is formed with two parallel bores 201 and 202. The bore 201 is formed with three longitudinally spaced annular grooves 203, 204 and 205, and receives a slidable valve member 206 which is manually operable.

The valve member 206 is formed with a centrally disposed reduced portion 207 which connects the two grooves 204 and 205 when the valve stem is positioned as illustrated in Fig. 6. The valve member 206 is retained in the position illustrated by means of a spring pressed detent 208 which engages with a groove 209 on the valve stem. The stem 206 is movable to the left as viewed in Fig. 6 to a position illustrated in Fig. 5 wherein the stem groove 207 connects the two valve bore grooves 203 and 204. In the latter position, the stem is retained by engagement of the detent 208 in a stem groove 210. Operation of the member 206 is obtained by a pivotally mounted handle'211 having a pin and slot connection 212 with the valve stem.

The valve bore 202 is formed with three spaced annular grooves 214, 215 and 216. A valve stem 217 is slidably positioned in the bore 202, and normally urged to the position illustrated in Fig. 6 by spring 218. In the position illustrated, a centrally disposed reduced portion 219 on the valve stem connects the bore grooves 215 and 216.

The groove 214 in the bore 202 connects with an outlet port 220 from the valve body adapted to be connected to a pressure conduit. The groove 214 also is connected by a passage 221 with the groove 203 in the bore 201. The groove 216 in the bore 202 is connected by a passage 222 to the groove 204 in the bore 201. The third groove 205 in the bore 201 is connected to a drain port 223 in the valve block. The third groove 215 in the valve bore 202 communicates through a laterally extending passage 225 (Fig. 7) and an adjustable needle valve 226 with an outlet port 227. The pressure port 220 in the valve block is connected by a passage 230 and a passage 231 with an enlarged end portion 232 of the valve bore 202 to supply fluid pressure to the end of the valve stem 217 for obtaining automatic operation of this valve.

As seen in Figs. 4 and 5, the pressure port 220 leading into the valve block 200 is connected by conduit 234 which is in turn connected with the pressure conduit 167, so that whenever the directional valve 18 is opened in either direction from neutral, pressure fluid is delivered to the valve block 200, to the valve grooves 214 and 203. Also, in Figs. 4 and 5, it will be seen that the outlet port 227 from the valve block 200 is connected by a conduit 235 and branch conduits 236 and 237 to supply fluid under pressure from the valve block to efiect movement of the control pistons and 165 in the motors 10 and 11. As seen in Fig. 1, the drain port 223 from the valve block 200 is connected by a conduit 239 with the drain conduit 129.

In operation, the valve members 206 and 217 are normally positioned as illustrated in Fig. 6, so that the control pistons 1-65 are connected to drain through the conduit 235, the port 227, stem groove 219, passage 222, stem groove 207, and conduit 223. With the direction valve positioned as illustrated in Fig. 4, the motors 10 and 11 are operated full speed in a forward direction. In the event that the motors encounter an undue resistance to turning, as when the wheels driven thereby encounter an obstruction or an incline, the resistance to turning causes a pressure rise in the pressure-conduit 147, in the passage 167, in the conduit 234, in the pressure port 220; inthe passages 203" and 213, and the valve bore 232; c The increased, pressure causes rflove'ment of the'valveniember 217 to ,t heposition Fig. 4, wherein the pressure port 220 is connected bythe'stem groove219 to the outlet port2'2'7 in the valveblock 200. Pressurefluid is thus applied to tlie'condnit and to actuate the control pistons: 165aand 1 65', -;shifting1the swash plates 164 and 164 to a maxirnurn an'gle providing maximum pump displacement, maximumtorque atthe motors, and minimum speed;

If the resistance of the moters ltlf andll to manecreases, there will be a pressure drop 'inthesystem which permits return of the valve member 217 to the normal position illustrated in 6, thereby connecting the coin tfrol pistons 165 todr'ain z This permits return of the swash plates to a minimum displacement angle providing high speed and minimurntorque. c H Manualcontrol ofthedisplacementof the motors is prdvided by shifting the valve mernber 20d from the nor: mal position illustrated Fig; 6 to the position illustrated Fig. 5. In the latterposition; pressure fluid is supplied to the control pistons 165 throughthe pressure p'o'rt-220; the passage 221-, stem groove 207, passage 2-22, stem groove 219, outlet port 227, and the conduit 235;

"Ihe operation of the automatic torque valve 217 is as follows. At a given flow-rate and pressure, the torque output of the engine 17 is absorbed by the pump 15, and the torque multiplication valve and the variable displacement motors permit these operating conditions'to remain constant, with the propelling motors operating at. a maximum speed with minimum torque output. When an obstruction' or a ramp is encountered, the system pressure would normally rise to meet the overloadcondition on the propelling motors; The tendency toward a pressure rise in the system is sensed by thevalve 217 to increase the displacement of the propelling motors'from a minimum displacement to a maximum displacement, While maintaining the system pressure constant; Increase in the motor displacement while holding the pressure and flow constant results in an increased torque delivery by the motors, the torque increasing in direct proportion with the displacement, and the speed of the motors varying inversely as the displacement of the motors. The lift truck on encountering a ramp" or the like thus automatically modulates speed and torque until the speed reduces to a minimum, and a torque-is provided. After the ramp is negotiated; the motors automatically regain speed when the overload conditien-is' eliminated.

Manual operation of the torque valve 206 enables an accurate control of the propelling motors at very low speeds. This valve, when shifted to the position of Fig. 5, holds the propelling motors in maximum displacement, resulting in speed and maximum torque at the drive wheels. The vehicle may thereby be inched along. The propelling motors, operating at maximum displacement, enable the truck to roll over an obstruction without a reduction in speed, the increased load to climb the obstruction producing merely a slight rise in system pressure; Thus, the operator is enabled to maintain precise speed control in close quarters regardless of the condition of the floor or terrain on which the truck is operated.

According to the present invention, manually controllablemeans is provided for braking theprope'lling motors when the lift truck is parked in neutral on an incline and to brake the propelling motors onslowdo wn to a stop.

Also, means is provided to automatically brake thepropelling motors at any time when the motors tendto overr'unrat a speed requiring a greater fluid flow through ,zinclined ramp or the like is encountered.

Referring now particularly" to; Fig. l, the "manually controllable dire'cuonal valve18 for-controlling the pro pellingmotors '11) and 11 includes valving for braking the propelling motors on slowdown and in neutral. Principally, the valvin'g referred to comprises" the' lands 152 and 154 on thevalve stem When the valve stem 150 positioned as illustrated in Fig. 1, the land 152 "serves to block the motor port 139, and the' land 154 serves to block the -motor port 140. Thus, h?- the truck is parked on an incline, facing either forwardly or reversely, the weight of the truck and any load carried thereby will tend to cause the truck to roll down the ramp. Such a condition causes the propelling motors 10 and ill to function as pumps. But, inasmuch as bothmotor ports 139 and 146 are blocked, the propelling motors; when rotated in either direction pump against a blocked passage. Obviously this restricts the flow of fluid fromthe motors, and brakes the motors.

Similarly, the valving described also functions tobrake the propelling motors on slowdown. Thus, if, whileopcrating the propelling motors fonwardly as describedin connection with Fig. 3, the valve stem 1'50 is;returned from the position illustrated in Fig; 3 toward the position illustrated inFig. 1, the valving described will function to brake themotors.

The operation isas follows. On slowdown, the flow of pressure fluid to the propelling motors'is reduced, thus tending to slow the motors.- But, the inertia of the rolling truck tends to maintain the truck, momentarily at least, at the initial speed. The motors thus being to function as pumps, pumping more fluid than that delivered to the motors, and pumping against the partially closed directional valve. Thus, the land 152 or the land 154, depending, on the direction of movement, tend to restrict the flow from the motors and to brake the motors. If the valve stem 15!? is moved completely to the neutral position the lands 152 and 154 completely blockthe flow from the motors as described previously.

The braking relief valve means 26, previously referred to in general, is provided to maintain the braking pressure in the motor return line 144 or 147, depending on the direction of truck movement. This valve means functions to bypass fluid from the motor return line to the motor inlet line to regulate the braking pressure and at the same time maintain hydraulic fluid in the braking circuit. I As seen in Fig. 1, for example, the braking valve means 26 includes a valve body 250 having a first conduit 251 connected to the motor conduit 144 and a second conduit 252 connected with the motor conduit 147. The valve body 250 is also provided withtwo valve bores, one bore housing a spring pressed check valve 253 biased to a closed position against the pressure of fluid in the conduit 251. The second bore houses a spring pressed check valve 254 biased to a closed position against the pressure of fluid in the conduit 252. Passages provided in the valve body enable the valve 253 to deliver fluid from the conduit 251 to the conduit 252, and additional passages enable the valve 254 to deliver fluid from the conduit 252 to the conduit 251.

In operation, assuming thestruck is parked in neutral, as illustrated in Fig. 1, on an incline such that the truck tends to roll forwardly, the motors 10 and 11 tend to function as pump-s, drawing fluid in through the motor conduit 147 and pumping the fluid out through the conduit 144. In this case, the land 152 blocks the flow of fluid from the motors, the valve 254 is held closed by its biasing spring and by the pressure of fluid in conduit 251, and the valve 253 is biased toward a closed position by its spring. The valve 253 will thus maintain the braking pressure in the line 144 up to a predetermined value, at which time the valve 253 will open. When the valve opens, the motor outlet line 144 is connected to the motor inlet line 147 to thereby return fluid to the motor inlets. The valve 253 thus functionsto regulate braking pressure and to provide a braking circuit and to maintain the braking circuit charged with fluid.

The braking relief valve 254 functions in a similar manner when the truck tends to roll rearwardly and the propelling motors thus tend to pump out the conduit 147 and to draw through the conduit 144. V

The setting on the braking relief valves 253 and 254 is high enough that these valves do not relieve system pressure when propelling. In a system wherein the constant system pressure maintained by the pump is about 1500 p.s.i., for example, the setting on the valve may be about 1600 p.s.i., for example. Thus, when the directional valve 18 is open, during propelling, the control valve 50 maintains the system pressure at 1500 p.s.i., and the braking relief valves 253 and 254 never open. When the directional valve 18 is positioned in neutral and valves 253 and 254 control braking, the constant pressure control valve 50 does not regulate pressure in the braking circuit. Instead, valves 253 and 254 control, and maintain pressure on the braking circuit.

If, during a braking operation, the propelling motors, while pumping, develop an excessively high pressure in the motor return line, over pressure relief valve means 27 is provided to relieve such pressures and maintain the same within safe limits. As illustrated, the over pressure relief valve means comprises a valve body 255 having an inlet 256 connected with the motor conduit 147 and an inlet 257 connected with the motor conduit 144. A spring pressed check valve 258 normally maintains the inlet 256 closed. A spring pressed check valve 259 normally maintains the inlet 257 closed. Both inlets 256 and 257 communicate with a spring biased over pressure relief valve 260 which is normally positioned by its biasing means to prevent the flow of fluid from the valve body to drain line 169.

In operation, if the operating condition is such that braking pressure is developed in the line 144 and increases to a predetermined excessively high value, say 1800 p.s.i., for example, in the circuit illustrated, valves 259 and 260 will be opened to relieve the braking pressure to drain line 169 Similarly, if an excessively high braking pressure develops in conduit 147, the check valve 258 and the relief valve 260 will open to relieve such pressure. When the pressure drops to a safe limit, these valves will close again. While the over pressure relief valve means has been illustrated as connected across the motor conduits 144 and 147, with check valves to regulate the flow to the relief valve, it will be apreciated that the desired function may be obtained by providing separate over pressure relief valves in each of the lines 144 and 147.

When the valve stem 153 of the directional valve 18 is positioned in neutral as illustrated in Fig. 1, under certain conditions, fluid lost from the braking circuit could be made up by leakage past the various valves to keep the braking circuit charged with fluid. Under other conditions, however, leakage past the valves may not be sufficient to maintain the braking circuit charged. Accordingly, means is provided to positively insure that the braking circuit is fully charged with fluid under all conditions to insure full braking.

The means to provide makeup fluid for the braking circuit includes the makeup valve means 28 previously referred to in general. When the valve stem 153 is positioned in neutral, fluid is supplied from the pump to the makeup valve through the pump delivery conduit 21, a passage 261 through the valve stem 153, and a conduit 262 which leads to a makeup valve inletport 263. The makeup valve 28 includes a valve body 264 formed with the inlet port 263 and with outlet ports 265 and 266. The outlet port 266 connects with a conduit 267 having a check valve 268 normally biased to a closed position preventing the flow of fluid to the motor port 140. The valve outlet port 265 connects with the conduit 269 having a check valve 270 normally biased to a closed posi, tion blocking the flow of fluid to the motor P 59,

A valve member 271, slidable in the makeup valve body 264 is formed with a passage 272 therethrough adapted to connect the valve inlet port 263 to the valve outlet ports 265 and 266. So long as the braking circuit is charged adequately with braking fluid, the pressure of fluid in the conduits 267 and 269 is sufficient to holdthe valve member 271 in the position illustrated in Fig. 1, blocking communication between the makeup valve inlet and outlet ports.

However, the makeup fluid from the pump is always available at the valve inlet port 263 when the valve stem 153 is positioned in neutral. Thus, in the event the braking circuit requires additional fluid, the pressure drop in the motor inlet line 147 or 144, depending on the direction of rotation of the motors, will drop permitting the check valve 270 or 268 to open, permitting a drop in the pressure in the conduit 269 or 267. In this event, a spring 274 forces the makeup valve member 271 to the left from the position illustrated in 'Fig. l, to a position in which the stem passage 272 connects the inlet port 263 and the outlet ports 265 and 266. Makeup fluid thereupon flows to the motor inlet conduit 147 or 144. The pressure of fluid in the motor outlet conduit will maintain one of the check valves 270 or 268 closed, depending on the direction of rotation. When the demand for makeup fluid is satisfied, the pressure of fluid on the left end of the valve member 271 will return the valve member to the position illustrated in Fig. 1.

The automatic braking valve means 29 includes means forming a valve bore 281 having an inlet port 282 and an outlet port 283. The inlet port 282 is connected with the conduit 284 which leads from the drain lines 168 and 169. The outlet port 283 is connected by a conduit 285 to the drain line 129 which leads to the reservoir 16. A valve member 287 is slidably disposed in the valve bore 281, and is formed with a central reduced portion 288 which serves to connect the valve inlet port 282 and the valve outlet port 283 when the valve member is positioned as illustrated in Fig. l. A spring 289 acts against the valve member 287, biasing the valve toward a position in which communication is blocked between the inlet port 282 and the outlet port 283. ,At the opposite end of the valve member from the spring 289, the valve bore is provided with a pressure port 290 which is connected by a conduit 291 with a pressure port 292 in the valve body of the directional valve 18.

In operation, at any time when the pump 15 is pumping, and the directional valve 18 is open, the pressure of fluid in the conduits 21, 167 and 291 is sufficient to maintain the valve member 287 in the position illustrated in Fig. 1, thereby placing the inlet port 282 and the outlet port 283 in communication. Thus, under normal operating conditions, when the propelling motors 10 and 11 are operated either forwardly or reversely, at either high speed or low speed, the return conduits from the motors are open to drain since the valve member 287 is positioned to connect the drain lines 284 and 285. These conditions are illustrated in Figs. 3 and 4.

If, under these conditions the truck encounters a downward incline, the motors 10 and 11 may tend to overrun at a speed requiring more flow through the motors than is delivered by the pressure source. In this case, the motors begin to function as pumps, drawing fluid from the pressure conduit 21 and pumping to the drain lines 284 and 285. Since the propelling motors are functioning as pumps and are requiring more fluid than that delivered by the pressure source, the pressure of fluid in the pressure conduit 291 drops, enabling the spring 289 to move the valve member 287 to the position illustrated in Fig. 10, blocking the flow of fluid from the conduit 284 to the conduit 285. Since the flow of fluid from the motors 10 and 11 is thereby restricted, the motors are braked down to a proper speed, after which the pressure of the operating fluid will rise again to the proper value, again opening the braking valve 287.

labinai We claim:

1. In a hydraulic system, a pair of variable'displacement hydraulic motors adapted for connection respectively with a pair of propelling wheels of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve for controlling the flow of pressure fluid from the source to the motors, means sensitive to a differential flow through the motors as a result of a differential resistance of the motors to turn, to increase the flow of pressure fluid to the motor having the greatest resistance and to decrease the flow of pressure fluid to the motor having the least resistance, fluid operable means for varying the displacement of the motors, valve and conduit means operable for connecting said dis placement varying means alternatively to drain or to pressure fluid therebyto vary the displacement of the motors between a high speed, minimum torque value and a low speed, maximum torque value, and conduit means connected with the motor outlets for conducting fluid therefrom to drain including valve means operable to restrict the flow of fluid from the motors to thereby brake the motors.

2. In a hydraulic system, a pair of variable displacement hydraulic motors adapted for connection respective- 1y with a pair of propelling wheels of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve movable between a neutral position blocking the flow of pressure fluidto the motors and an operative position connecting said source and the motors, valve means sensitive to a differential flow through thernotors, as a result of a differential resistance of the motors to turn, to increase the flow of pressure fluid to the motor having the greatest resistance, and to decrease the flow of pressure fluid to the motor having the least resistance, fluid operable means for varying the displacement of the motors normally positioned to provide a high speed, minimum torque displacement, valve means normally positioned to connect said displace ment varying means to drain and responsive to increased resistance of the motors to turn to connect said displacement varying means to pressure fluid to increase the dis placement of the motors to a low speed, maximum torque value, valve means normally positioned to connect said displacement varying means to drain and manually operable to connect the displacement varying means to pressure fluid to increase the displacement of the motors to a low speed, maximum torque value, valving on said directional valve for restricting the flow of fluid from said motors when the directional valve is positioned in neutral to thereby brake the motors on slowdown and when the directional valve is positioned in neutral, andvalve means subjected to pressure fluid from said source and thereby positioned to connect the-motor outlets to drain, said last recited valve means being operable, upon a drop in the pressure of fluid from said source whenever the motors tend to overrun at a speed requiring more flow than that provided by the source, to restrict the flow from said motors to drain to thereby brake the motors.

3. In a hydraulic system, a pair of hydraulic motors adapted for connection respectively with a pair of propelling wheels of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve for controlling the flow of pressure fluid from the source to the motors, means sensitive to a difierential flow through the motors, as a result of a differential resistance of the motors to turn, to increase the flow of pressure fluid to the motor having the greatest resistance and to decrease the flow of pressure fluid to the motor having the least resistance, and conduit means connected with the motor outlets for conducting fluid therefrom to drain including valve means operable to restrict the flow of fluid from the motors to thereby brake the motors.

4.ln a hydraulic system, a variable displacement bydraulic motor adapted for connection with a propelling 18 wheel of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve for controlling the flow of pressure fluid from the source to the motor, fluid operable means for varying the displacement of the motor normally biased toward a minimum displacementposition, valve means normally positioned for connecting said displacement varying means to drain and responsive to increased resistance of the motor to turn to connect the'displacement varying means to pressure fluid thereby to increase the displacement of the motor from a high speed, minimum torque value to a low speed, maximum torque value, and conduit means connected with the motor outlet for conducting fluid therefrom to drain including valve means operable to restrict the flow of fluid from the motor to thereby brake the motor.

5. In a hydraulic system, a pair'of variable displacement hydraulic motors adapted for connection respectively with a pair of propelling wheels of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve for controlling the flow of pressure fluid from the source to the motors, means sensitive to a differential flow through the motors, as a result of a difierential resistance of the motors to turn, to increase the flow of pressure fluid to the motor having the greatest resistance and to decrease the flow of pressure fluid to the motor having the least resistance, fluid operable means for varying the displacement of the motors, valve and conduit means operable for connecting said displacement varying means alternatively to drain or to pressure fluid thereby to vary the displacement of the motors between a high speed, minimum torque value and a low speed, maximum torque value.

6. In a hydraulic system, a variable displacement hydraulic motor adapted for connection with a propelling Wheel of a vehicle, means providing a source of operating fluid under pressure, a pressure conduit for conductthe displacement of the motor to a low speed, high torque value. p

7. In a hydraulic system, a variable. displacement hydraulic motor adapted for connection with apropelling wheel of a vehicle, means providing a source of operating fluid under pressure, a pressure conduit for conducting pressure fluid from the source to the motor inlet,

r fluid operable means for varying the displacement of the motor, means normally biasing the displacement varying means to provide a high speed, low torque displacement, and torque valve means normally positioned to connect the displacement varying means to drain and manually operable to connect the displacement varying means to said pressure conduit to increase the displacement of the motor to a low speed, high torque value.

'8. In a hydraulic system, a'variable displacement hydraulic motor adapted 'for connection with a propelling wheel of a truck or the like, means providing a source of operating fluid under pressure, a pressure conduit for conducting pressure fluid from the source to the motor inlet, fluid operable means for varying the displacement of the motor, means. normally biasing the displacement vary-ing means to a minimum displacement position providing high speed and minimum torque for the motor, a valve normally positioned to connect the displacement varying means to drain and responsive to increased pressure in the conduit as a result of increased resistance 19 .of the motor to turn to connect said displacement vary ing means to the pressure conduit to cause movement of the displacement varying means to a low speed, maximum torque position, and a second valve normally positioned to connect said displacement varying means to drain and manually operable to connect the displacement varying means to the pressure conduit to increase the displacement of the motor to a low speed maximum torque value.

9. In a hydraulic system, a variable displacement hydralic motor adapted for connection with a propelling wheel of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve having an inlet port connected to said source of pressure fluid, an outlet port connected to the motor inlet, and a valve member movable between a closed position blocking communication between said valve ports and an open position vconnecting said valve ports, fluid operable means for varying the displacement of said motor, means normally biasing said displacement varying means to a minimum displacement position providing high speed and low torque for the motor, a torque valve normally positioned to connect the displacement varying means to drain, and valve means incorporated in said direc- .tional valve for subjecting the torque valve to the pressure of fluid at the valve outlet port when the directional valve is open, said torque valve being responsive to an increase of pressure at the directional valve outlet due to increased resistance of the motor to turn to connect said displacement varying means to pressure fluid to increase the displacement of the motor to a low speed, maximum torque value.

=10. In a hydraulic transmission, a reversible variable displacement hydraulic motor adapted for connection with a propelling wheel of a truck or the like, means providing a source of operating fluid at constant pressure, a directional valve having an inlet connected with the source of pressure fluid, a pair of motor ports connected respectively with the motor inlet and motor outlet, and a valve member having a neutral position block-ing the inlet port and two operative positions in opposite directions from neutral respectively for connecting either motor port to the inlet port so that the motor may be operated forwardly or reversely, fluid operable means for varying the displacement of the motor, means normally biasing the displacement varying means to a minimum displacement position providing high speed and low torque for the motor, a torque valve normally positioned to connect the displacement varying means to drain, valve means incorporated in said directional valve for subjecting the torque valve to outlet pressure at the directional valve when the directional valve member is moved to either operative position, said torque valve being responsive to increases in outlet pressure at the directional valve and movable thereby to a position connecting said displacement varying means to pressure fluid to cause movement of the displacement varying means to a low speed, maximum torque position.

11. In a hydraulic system, a pair of hydraulic motors adapted for connection respectively with a pair of propelling wheels of a truck or the like, means providing a source of operating fluid under pressure, conduit means and selectively operable valve means connected with the source of pressure fluid and with the motors including a first main conduit and a first pair of branch conduits connecting the valve means to the motor inlets and a second main conduit and a second pair of branch conduits connecting the valve means to the motor outlets so that the motors may be operated forwardly or reversely, and control valve means positioned in one pair of said branch conduits sensitive to a differential resistance of said motors to turn to restrict the passage area of both branch conduits of said one pair equally thereby to decrease the flow through the motor having the least resistance and to increase the flow through the motor having the greatest resistance.

12. The combination as defined in claim 11, wherein said control valve means comprises: a valve body having a first port connected with one of said main conduits and second and third ports connected respectively with the pair of branch conduits associated with said one main conduit, valving for controlling flow from said first port to ai se and third P t n f om he secon n third ports to the first port including a movable valve member normally positioned in a neutral center position enabling predetermined maximum equal flows in either direction through both motors, said movable valve memher having opposite ends respectively sensitive to fluid pressure in said one pair of branch conduits and movable in response to a pressure difierential in said one pair of branch conduits for equally restricting the passage areas connecting said first port to said second and third ports, whereby flow through the lightly loaded motor is restricted to a value substantially less than the capacity of said source, thereby enabling a substantial flow through the heavily loaded motor.

13. The combination as defined in claim 11, wherein said control valve means comprises: a valve body having a first port connected with one of said main conduits and having second and third ports connected respectively with the pair of said branch conduits associated with said one main conduit, a valve bore connecting said second and third ports, a pair of parallel flow divider passages both opening into said firstport and into said valve bore, a valve member slidable in' said valve bore, spring means normally biasing said valve member to a neutral center position placing said flow divider passages respectively in open communication with said second and third ports thereby to enable predetermined maximum equal flows through said motors in either direction, opposite ends of said valve member being exposed respectively to fluid in said one pair of branch conduits whereby a pressure differential in said one pair of branch conduits causes movement of the valve member to a position restricting tht flows through said flow divider ports equally, thereby to reduce the flow through the lightly loaded motor to a value substantially less than the capacity of said source thereby to enable a substantial flow through said heavily loaded mot r- 14. The combination as defined in claim 11, wherein said control valve means comprises: a valve body having a first port connected with one of said main conduits and having second and third ports connected respectively with the pairof said branch conduits associated with said main conduit, a valve bore connecting said second and third ports, a Pair of flow divider passages both opening into said first port and into said valve bore, a valve member slidable in said valve bore, spring means normally biasing said valve member to a neutral center position respectively placing said flow divider passages in open communication with said second and third ports thereby to enable predetermined maximum equal flows through said motors in either direction, opposite ends of said valve member being exposed respectively to fluid in said one pair of branch conduits whereby a pressure differential in said one-pair of branch conduits causes movement of the valve member to a position blocking flow through said flow divider passages, and a pair of by-pass passages respectively-connecting said second and third ports to said first port, and manually adjustable valve means in said by-pass passages for restricting the flow through said lightly loaded motor to a flow substantially less than the capacity of said source, thereby leaving a substantial volume of'fluid for the heavily loaded motor.

15. In a hydraulic system, a pair of hydraulic motors adapted for connection respectively with a pair of propelling wheels of a truck ,or the like, means providing a source of operating fluid under pressure, a directional valve having an inlet port connected with the source of wan conduits connecting one motor port to the motor inlets and second conduit means'including a main conduit and a pair of branch conduits connecting the other motor port to the motor outlets so that the motors may be operated forwardly or reversely, and control valve means positioned in one pair of said branch conduits sensitive to a differential resistance of said motors to turn to restrict the passage area of both branch conduits of said one pair equally thereby to decrease the flow through the motor having the least resistance and to increase the flow through the motor having the greatest resistance.

16. In a hydraulic system, a hydraulic motor adapted for connection with a propelling wheel of a vehicle, means providing a source of fluid under pressure, a'pressure conduit connecting the source and the motor inlet, a directional valve in said pressure conduit movable from a neutralposition blocking said pressure conduit to a nonblocking position permitting flow of pressure fluid to the motor, a return conduit connecting the motor' outlet to drain, braking valve means in the return conduit operative to restrict the flow of fluid from the motor to drain when the directional valve is in neutral position thereby to brake the motor, a cross conduit connecting to the pressure conduit between the directional valve and the motor and "connected to the return conduit between the motor and said braking valve means, a braking relief valve in said cross conduit normally biased, to a closed position blocking the crossconduit to maintain braking pressure in the return conduit, said braking relief valve being subjected to pressure fluid in the return conduit and movable thereby upon a rise in braking pressure in the return line above a predetermined value to connect the return line and the pressure line thereby to bypass fluid to the motor inlet to regulate the braking pressure and maintain fluid in the braking circuit;

17. The combination defined in claim 16, including makeup valve means for supplying fluid from the pressure conduit ahead of the directional valve to the pressure conduit between the directional valve and the motor when the directional valve is positioned in neutral to thereby maintain the braking circuit charged with fluidu 18. The combination as defined-in claim 17, wherein said makeup valve means comprisesza valve inlet communicating with the pressure conduit ahead of the, direcfluid in said makeup conduit between the valve outlet and-the check valve urging said movable valve member toward a position blocking communication between the valve inlet and valve outlet, a drop in pressure in said pressure conduit between the directional valve and the motor when said directional valve is closed permitting said check valve to open thereby enabling movement of said valve member to a position connecting the pressure conduit ahead of the directional valve to the braking circuit.

19. The combination defined in'claim 16, including an over-pressure relief valve connected to the return conduit and ,to drain, means normally biasing the over-pressure relief valve to a closed position blocking communication between, the return conduit and drain, said over-pressure relief valve being subjected to pressure in the return con- Quit toopen and connect the return conduit to drain upon an increase in braking-pressure in the return conduit to a predetermined excessively high value. 20. The combination defined in claim 18, including makeup valve means for supplying fluid from the pressure conduit ahead of the directional valve to the pressure conduit between the directional valve and the motor when the directional valve is positioned in neutral to thereby maintain the braking circuit charged with fluid.

21. In a hydraulic system, a reversiblehydraulic motor adapted for connection with a propellingwheel of a truck or the like, means providing a source of fluid at constant pressure, a directional valve having an inlet port connected with the source of pressure fluid, a pair of outlet ports connected to drain, a pair of motor ports, and a movable valve member having a neutral position blocking communication of the inlet port with both motor ports and two operative positions in opposite directions from neutral respectively for connecting either motor port to the inlet port and the other motor port to a drain port, a first conduit connecting one motor port to a motor inlet and a second conduit connecting the other motor port to the motor outlet so that the motor may be operated forwardly or reversely, and braking valve means operable to block the flow of fluid from the motor to drain thereby to brake the motor, comprising, a braking valve having an inlet port connected to the drain ports of said directional valve and an outlet port connected to drain, said braking valve including a braking valve member and means biasing the same toward a position blocking communication between the braking valve inlet and outlet ports, conduit means for subjecting the braking valve member to pressure fluid when the directional valve member is in'either operative-position thereby to position the braking valve member to connect the braking valve inlet and outlet ports, said biasing means being operable, upon a drop in the pressure of fluid in said pressure conduit whenever the motor tends to overrun at a speed requiring more flow than that provided by the source, to move said braking valve member to a position blocking the flow from said motor thereby to brake the motor;

22. In a hydraulic system, a hydraulic motor adapted for connection with a propelling wheel of a vehicle, a second hydraulic motor adapted for connection with auxiliary vehicle equipment, a variable displacement pump in fiuid communication with the motors, selectively operable valve means for controlling the flow of operating fluid under pressure from the pump to the motors to selectively supply neither motor, either rno tor separately, or both motors simultaneously, aprime mover fordriving the pump, means for varying the pump displacement to maintain pump outlet pressure'constant regardless of whether the selectively operable valve means is positioned to supply neither motor, either motor or both motors, and means responsive directly to the volumetric flow rate in the pump outlet for varying the speed of the prime mover as the flow rate varies, comprising, a fuel feed device for regulating the flow of fuel to the prime mover, means biasing said fuel feed device to a normal idling position, a restrictive orifice positioned in the pump outlet, and means responsive to the pressure drop acrossthe orifice for regulating said fuel feed device-to increase the speed of the prime mover on increases in said pressure drop and todecrease the speed of the'prime mover on decreases in said pressure drop.

23. In a hydraulic system, a hydraulic motor adapted for connection with a propelling wheel of a truck or the like, means providing a source of operating fluid at constant pressure, a pressure conduit connecting the source and the'motor inlet, a directional valve in said pressure conduit movable from a neutral position blocking said motor on slowdown and when the directional valve is in neutral, a valve member subjected to pressure fluid from said pressure conduit when saiddirectional valve is in non-blocking position and thereby positioned to connect the motor outlet to drain, means biasing said valve member toward a position blocking the motor return conduit, said valve member being operable by said biasing means, upon a drop in pressure of fluid in said pressure conduit when said directional valve is in non-blocking position and the motor tends to overrun at a speed requiring more flow than that provided by the source, to restrict the flow from said motor thereby to brake the motor, a cross .conduit connecting the pressure conduit and the return con-' duit at a point ahead of the braking valve means, and a braking relief valve in said cross conduit normally biased to a closed position blocking the cross conduit to maintain braking pressure in the return conduit, said braking relief valve being subjected to pressure fluid in the return conduit and movable thereby upon a rise in braking pressure in the return line above a predetermined value to connect the return line and the pressure line thereby to bypass fluid to the motor inlet to regulate the braking pressure and maintain fluid in the braking circuit.

24. The combination defined in claim 23, including an over-pressure relief valve connected to the return conduit and to drain, means normally biasing the over-pressure relief valve to a closed position blocking communication between the return conduit and drain, said over-pressure relief valve being subjected to pressure in the return conduit to open and connect the return conduit to drain upon an increase in braking pressure in the return conduit to a predetermined excessively high value.

'25. The combination defined in claim 23, including makeup valve means for supplying fluid from the pressure conduit ahead of the directional valve to the pressure conduit between the directional valve and the motor when the directional valve is positioned in neutral to thereby maintain the braking circuit charged with fluid.

26. In a hydraulic system for mobile equipment, a hydraulic motor, means providing a source of fluid under pressure comprising a variable displacement pump, a variable speed prime mover for driving the pump, means for varying the pump displacement to meet varying demands of the motor, and means for sensing the flow rate between the pump and the motor and varying the speed of the prime mover as the flow rate varies, comprising, a fuel feed device for regulating the flow of fuel to the prime mover, means biasing said fuel feed device to a normal idling position, a restrictive orifice positioned in the pump discharge line, and means responsive to the pressure drop across said orifice for regulating said fuel feed device to increase the speed of the prime mover on increases in said pressure drop and to decrease the speed of the prime mover on decreases in said pressure drop.

27. In a hydraulic system, a hydraulic motor, a variable displacement pump having an outlet in fluid communication with the motor inlet, selectively operable valve means for controlling the flow of fluid from the pump to the motor, means for continuously maintaining fluid in the pump outlet at constant pressure regardless of the position of theselectively operable valve means in cluding a control responsive to fluid pressure in the pump outlet for increasing pump displacement on decrease of pump outlet pressure and for decreasing pump displacement on increase of pump outlet pressure, a prime mover for driving the pump, and means responsive directly to the volumetric flow rate in the pump outlet for increasing the speed of the prime mover on increase of flow rate and for decreasing the speed of the prime mover on decrease of flow rate. Y

28. In a hydraulic system, a hydraulic motor, a variable displacement pump in fluid communication with the motor, fluid operable means for varying the pump displacement normally urged toward a minimum displacement position, selectively operable valve means control,-

ling the flow of fluid from the pump to the motor, and valve means for continuously maintaining constant pressure at the pump outlet, comprising, a valve responsive to fluid pressure at the pump outlet for controlling the flow of pressure fluid to and from the displacement varying means to increase pump displacement on decrease of pump outlet pressure and to decrease pump displacement on increase of pump outlet pressure including a valve housing having a pressure port in fluid communication with the pump outlet, a drain port, and a control port in fluid communication with the displacement varying means, a valve member in the housing having one end exposed to the pressure port and a passage through the valve member connecting the opposite end thereof to the pressure port, and spring means acting in conjunction with fluid pressure at said opposite end of the valve member urging the valve member toward a position blocking communication between the control port and the drain port and placing the control port in communication with said valve member passage at said opposite end of the valve, to increase pump displacement, fluid pressure at said one end of the valve member urging the valve member toward a position blocking communication between the valve member passage and the control port and placing the control port in communication with the drain port, to decrease pump displacement.

29. Valve means for controlling the flow of pressure fluid to and from a pump displacement varying means, comprising, a valve housing having a pressure port, a drain port, and a control port, a valve member in the housing having one end exposed to the pressure port and a passage through the valve member connecting the opposite end thereof to the pressure port, and spring means, acting in conjunction with fluid pressure at said opposite end of the valve member urging the valve member to a position blocking communication between the control port and drain port and placing the control port in communication with said valve member passage at said opposite end of the valve member, fluid pressure at said one end of the valve member urging the valve member toward a position blocking communication between the valve member passage and the control port and placing the control port in communication with the drain port.

30. A control valve, comprising, a valve body having a first port connectable to a. main conduit and having second and third ports connected respectively with a pair of branch conduits, a valve bore connecting saidsecond and third ports, a pair of parallel flow divider passages both opening into said first port and into said valve bore, a valve member slidable in said valve bore, spring means normally biasing said valve member to a neutral center position placing said flow divider passages respectively in open communication with said second and third ports thereby to enable predetermined maximum equal flows through said second and third ports in either direction, opposite ends of said valve member being exposed respectively to fluid in said second and third ports whereby a pressure differential in said second and third ports causes movement of the valve member to a position restricting the flows through said flow divider ports equally.

31. A control valve, comprising, a valve body having a first port connectable with a main conduit and having second and third ports connecta'ole respectively with a pair of branch conduits, a valve bore connecting said second and third ports, a pair of flow divider passages both opening into said first port and into said valve bore, a valve member slidable in said valve bore, spring means normally biasing said valve member to a neutral center position respectively placing said flow divider passages in open communication with said second and third ports thereby to enable predetermined maximum equal flows through said second and third ports in either direction, opposite ends of said valve member being exposed respectively to fluid in said second and third ports whereby 25 a pressure differential in said second and third ports causes movement of the valve member to a position blocking flow through said flow divider passages, and a pair of bypass passages respectively connecting said sec- 0nd and third ports to said first port, and manually adjustable valve means in said by-pass passages for restricting the flow therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 26 Ernst Apr. 30, 1935 Ernst et a1. June 25, 1935 Kendrick Apr. 15, 1941 Kendrick Apr. 15, 1941 Howell June 1, 1943 Boyle Aug. 17, 1943 Herman et a1. Sept. 7, 1943 Herman et a1. Sept. 7, 1943 Stephens Ju1y 1, 1947 Griflith Aug. 9, 1949 Norelius et a1. Jan. 5, 1954 Ferris Dec. 18, 1956 

